1. Field of the Invention
The present invention relates to a plasmon generator for use in thermally-assisted magnetic recording to write data on a recording medium with the coercivity thereof lowered by irradiating the recording medium with near-field light, and to a thermally-assisted magnetic recording head including the plasmon generator.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider configured to slightly fly above the surface of a recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, disadvantageously reduces the thermal stability of magnetization of the magnetic fine particles. To resolve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, thus making it difficult to perform data writing with existing magnetic heads.
To resolve the foregoing problems, there has been proposed a technology called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
U.S. Pat. Nos. 8,711,663 B1, 8,848,494 B2 and 8,861,138 B2 each disclose a thermally-assisted magnetic recording head including a main pole, a waveguide and a plasmon generator. The main pole has an end face located in the medium facing surface, and produces a write magnetic field from this end face. The plasmon generator has an end face located in the medium facing surface. The waveguide includes a core and a cladding. In this head, the surface of the core and the surface of the plasmon generator face each other with a gap interposed therebetween. This head is configured to excite surface plasmons on the plasmon generator by using evanescent light that is generated at the surface of the core from the light propagating through the core, and to generate near-field light from the excited surface plasmons at the end face of the plasmon generator.
To achieve higher recording density, it is necessary to make the track width smaller by reducing at least one of the width of the end face of the plasmon generator in the medium facing surface and the width of the end face of the main pole in the medium facing surface.
In a thermally-assisted magnetic recording head, heat generated by the plasmon generator causes the plasmon generator to get hot. This results in the problem of deformation or breakage of the plasmon generator, thus shortening the life of the thermally-assisted magnetic recording head. In particular, the smaller the width of the end face of the plasmon generator in the medium facing surface, the more noticeable the aforementioned problem becomes.
One of solutions to the aforementioned problem is to construct the plasmon generator to include a first metal portion and a second metal portion that are formed of mutually different metal materials, as disclosed in U.S. Pat. Nos. 8,711,663 B1, 8,848,494 B2 and 8,861,138 B2. The first metal portion has an end face located in the medium facing surface. The second metal portion has a front end that is closest to the medium facing surface and located at a distance from the medium facing surface. The second metal portion further has a plasmon exciting section to excite surface plasmons thereon. The surface plasmons excited on the plasmon exciting section propagate to the end face of the first metal portion located in the medium facing surface, and near-field light is generated from those excited surface plasmons at the end face of the first metal portion.
A metal suitable for excitation and propagation of surface plasmons, that is, a metal having high electrical conductivity such as Au or Ag is selected as the metal material to form the second metal portion. As the metal material to form the first metal portion, selected is one having higher hardness than the metal material used for the second metal portion. This serves to prevent the first metal portion from being deformed or broken.
However, the plasmon generator including the aforementioned first and second metal portions has a problem in that the heat generated at the first metal portion is transferred to the second metal portion to cause the second metal portion to get hot, and can thus deform the second metal portion such that its front end gets farther from the medium facing surface.